Ceramides are an important group of lipids, members of which are found in the epidermis of mammals. Skin ceramides are believed to play an important role in the water permeability properties of the skin, providing an epidermal water-barrier which functions to give increased strength to the skin structure and to decrease water loss and so improve the condition of the skin.
Ceramides are N-acylated sphingosine bases. Sphingosine bases are of variable chain length and have the general formula (i): EQU CH.sub.3 (CH.sub.2).sub.x ACHOHCH(NH.sub.2)CH.sub.2 OH (i)
where A is --CH.dbd.CH-- (sphingosine), --CH.sub.2 CHOH--(phytosphingosine) or --CH.sub.2 CH.sub.2 -- (dihydrosphingosine), and where x is generally in the broad range 7 to 27, more typically in the range 10 to 16. It should be noted that sphingosines contain asymmetric carbon atoms and so various stereoisomers are possible. Sphingosine/ceramides from especially mammalian sources are all the D-erythro isomer and phytosphingosine/phytoceramides the D-D-erythro isomer. Seven distinguishable groups of ceramides have been identified in pig and human epidermis. Each group consists of molecules of varying fatty acid chain length. The structures of typical skin ceramides are described in the paper entitled "Ceramides of Pig Epidermis: Structure Determination" by P. W. Wertz and D. T. Downing in Journal of Lipid Research, Vol 24, 1983, pages 759-765.
Because of their properties it is known to use ceramides, ceramide derivatives and also pseudoceramides (synthetic molecules which have properties similar to those of naturally occurring ceramides) as components of skin care compositions.
It is difficult to extract ceramides from natural sources, and in some cases the resulting product is not acceptable for cosmetic compositions. Furthermore, ceramides are difficult and expensive to synthesise chemically.
It has been proposed in EP 0 097 059 to synthesise N-[omega-(O-linoleoyl) 23-cis-dotriacontenoyl] sphingosine by chemically synthesising an appropriate sphingosine component and linking this to an appropriate acid.
The paper "Formation of Extracellular Sphingolipids by Microorganisms" by H. G. Maister et. al. in Appl Microbiol vol 10, page 401 to 406 describes a process for producing tetraacetyl phytosphingosine (TAPS) from the F-60-10 mating type strain of the yeast Hansenula ciferrii. This process uses glucose as a carbon source in a batch mode fermentation at 25.degree. C. The process, however, is not very efficient, and while it can yield sufficient TAPS for experimental purposes the yield is too low to be practicable for commercial purposes. The TAPS produced is the D-D-erythro isomer, the same as occurs in human skin.
The present inventors have derived a modified process for producing TAPS from Hansenula ciferrii that is much more efficient and which is then used as a component of commercial production of phytosphingosine-containing ceramide one.